Magnetic recording tapes are widely used in recording sound and electrical signals, as in video recorders, computers and data processing and recording machines and the like. Such tapes typically consist of a thin plastic backing tape coated with a solid plastic matrix in which is embedded finely powdered particles of a magnetizable material. See, for example Schnell, et al., U.S. Pat. No. 3,505,109 and Diaz, U.S. Pat. No. 3,437,510.
A great deal of work has been done in the magnetic tape art to improve the uniformity and density of the magnetic coating. This has largely been directed to using smaller and more uniform magnetic particles and to improving the density and uniformity of their distribution in the plastic matrix or binder layer. Another highly desirable objective has been to devise a coating composition that can be applied from an aqueous medium, thus avoiding the problems that arise from the use of organic solvents, such as high cost, toxicity to workers, pollution of the environment, etc.
Hatch, et al., U.S. Pat. Nos. 3,636,052, 3,660,431 and 3,749,737, 3,749,738 and 3,749,739 describe cyclic sulfonium zwitterionic compounds that readily polymerize to produce solid plastics that are useful as coating materials.
Schmidt, et al., U.S. Pat. No. 3,813,363, describe the use of the Hatch, et al. compounds as coating materials into which various particulate solids, such as silica, silicone oils, iron oxide, alumina, magnesium oxide, barium sulfate, calcium carbonate, titanium dioxide, synthetic rubber and polytetrafluoroethylene, are incorporated and coatings are made therefrom.
Broxterman, et. al., U.S. Pat. No. 3,804,797 disclose compositions comprising the above Hatch, et al., compounds and a water-soluble anionic polymer containing a plurality of carboxyl groups (which latter may be in ammonical salt form). Such compositions are useful as coating materials since they may be prepared in aqueous or organic solvent medium, applied to a substrate, dried to a solid film, and then, if desired, cured to a water-resistant and solvent-resistant coating by a brief, mild heat treatment.